This invention relates to automatic transmissions, and particularly to computer controlled step transmissions suited for small vehicle engines
Automatic transmissions are universally appreciated for the convenience they afford in operating vehicles Such transmissions are employed most frequently in larger vehicles such as automobiles, because they require power and space not always available in vehicles with smaller engines. Step transmissions for small vehicles tend to be manual. For example, U.S. Pat. No. 4,339,964 (Isaka), assigned to the assignee of this application, shows an internal combustion engine for a motorcycle, in which a crank shaft and transmission are positioned one above the other to minimize the required size of the engine. A gear shift pedal is pivotable manually in opposite directions for shifting to either a higher or lower gear. A torsion spring returns the pedal to substantially the same rest position after each shift.
An alternative small vehicle transmission is disclosed in U.S. Pat. No. 4,027,544 (Kobayashi), also owned by the present assignee. A sliding sheave is moved continuously closer to an axially fixed sheave on a driving shaft, thus to position a V-belt gradually radially outward as driving shaft velocity increases. While this arrangement continuously and smoothly changes the gear ratio, it lacks the power transmitting efficiency of step transmissions. Automatic step transmission systems are being developed in the automobile industry. Typically, these systems control hydraulic power actuators through a computer. These systems, however, are complex and require auxiliary power for the hydraulic actuators, power typically not conveniently available in smaller engines. In addition, automatic transmissions for certain recreational vehicles, for example all-terrain vehicles or four-wheel drive vehicles, must adapt to unique conditions, for example hill climbing, rarely encountered by ordinary passenger automobiles. Thus there is a general tendency to favor manual transmissions in such vehicles.
Therefore, it is an object of the present invention to provide an automatic step transmission suitable for use with small internal combustion engines.
Another object of the invention is to provide an automatic step transmission for small vehicles that uses the normal engine manifold vacuum as its power source.
Another object is to provide, in an internal combustion engine for a small vehicle, a transmission that affords smooth shifting without undue sacrifice in transmitted power.
Yet another object of the invention is to provide an automatic step transmission that adapts to the wide variety of conditions encountered by all-terrain vehicles and the like.